This invention relates to method and apparatus for producing sound at very high intensities, typically above 160 db, for use in a variety of applications, especially in acoustic levitation devices.
In conventional sound producing devices, a diaphragm or piston may be caused to vibrate in a sound transmitting medium such as air to produce sound waves. One form of transducer used for producing high intensity sounds is referred to as a St. Clair device. In such a device, a resonant, half wavelength matallic stub or bar is electromagnetically driven, which causes the stub to elastically expand and contract in a resonant mode and propagate sound waves away from the ends, and long the axis of the stub. The electromechanical drive may be in the form of discs of piezoelectric material which are firmly compressed between the two parts of the bar.
While the St. Clair sound source if capable of relatively high intensity sound output, i.e., up to 160 db, the design is troubled with problems of low efficiency, large input power requirements, and poor fatigue resistance.
High intensity sound sources are particularly useful for acoustic levitation, in which sound waves are used to suspend or hold an object in position without any other means of support. As described in U.S. Pat. No. 4,284,403, acoustic levitation has been considered most practical for use in space because considerable acoustic power is required to overcome the force of gravity on earth acting on the levitated object. A more efficient and intense source of sound would allow for acoustic levitation of higher density objects on earth, or would allow use of such devices in space with greater reliability and less consumption of electrical power.